Use of a bioactive scaffold to stimulate anterior cruciate ligament healing also minimizes posttraumatic osteoarthritis after surgery

Abstract

Background: Although anterior cruciate ligament (ACL) reconstruction is the treatment gold standard for ACL injury, it does not reduce the risk of posttraumatic osteoarthritis. Therefore, new treatments that minimize this postoperative complication are of interest. Bioenhanced ACL repair, in which a bioactive scaffold is used to stimulate healing of an ACL transection, has shown considerable promise in short-term studies. The long-term results of this technique and the effects of the bioenhancement on the articular cartilage have not been previously evaluated in a large animal model.

Hypotheses: (1) The structural (tensile) properties of the porcine ACL at 6 and 12 months after injury are similar when treated with bioenhanced ACL repair, bioenhanced ACL reconstruction, or conventional ACL reconstruction, and all treatments yield results superior to untreated ACL transection. (2) After 1 year, macroscopic cartilage damage following bioenhanced ACL repair is similar to that in bioenhanced ACL reconstruction and less than in conventional ACL reconstruction and untreated ACL transection.

Study design: Controlled laboratory study.

Methods: A total of 64 Yucatan mini-pigs underwent ACL transection and randomization to 4 experimental groups: no treatment, conventional ACL reconstruction, bioenhanced ACL reconstruction using a bioactive scaffold, and bioenhanced ACL repair using a bioactive scaffold. The biomechanical properties of the ligament or graft were examined and macroscopic assessments of the cartilage surfaces were performed after 6 and 12 months of healing.

Results: The structural properties (ie, linear stiffness, yield, and maximum loads) of the ligament after bioenhanced ACL repair were not significantly different from those in bioenhanced ACL reconstruction or conventional ACL reconstruction but were significantly greater than those in untreated ACL transection after 12 months of healing. Macroscopic cartilage damage after bioenhanced ACL repair was significantly less than that in untreated ACL transection and bioenhanced ACL reconstruction, and there was a strong trend (P = .068) for less macroscopic cartilage damage than in conventional ACL reconstruction in the porcine model at 12 months.

Conclusion: Bioenhanced ACL repair produces a ligament that is biomechanically similar to an ACL graft and provides chondroprotection to the joint after ACL surgery.

Clinical relevance: Bioenhanced ACL repair may provide a new, less invasive treatment option that reduces cartilage damage following joint injury.

Keywords: anterior cruciate ligament; collagen; osteoarthritis; platelet; reconstruction.

Fig. 1

Four treatment groups were evaluated in this study: A) ACL transection, B) conventional ACL reconstruction, C) bio-enhanced ACL reconstruction, and D) bio-enhanced ACL repair.

Fig. 2

The mean differences between limbs (Surgical-Intact) for A) linear stiffness, B) yield load, and C) maximum load for the four experimental groups (ACLT=ACL transection, ACLR=ACL reconstruction, BE-ACLR=bio-enhanced ACL reconstruction and BE-Repair=bio-enhanced ACL repair) at 6 and 12 months. The mean data are plotted with the 95% confidence intervals. A value of zero indicates that the yield or maximum failure loads are equal between legs. Means that do not differ between groups after Holm adjustment within each time point have the same lower case letter (a or b).

Fig. 3

Histological examination of the ACL and replacement tissues 6 and 12 months after surgery. The intact ACLs had relatively sparse cells and vasculature (A & H). In contrast, all three experimental groups had a much higher cell density throughout the ACL tissue 6 months post-opeartively (B, C and D). The hypercellularity in all groups decreased by 12 months, but the experimental groups still appeared to have a greater number of cells within the tissue than the intact ACL knee (E, F & G). In terms of vascularity, the bio-enhanced ACLR group had a vascularity pattern similar as seen in the intact ACL at both 6 and 12 months (Figure J and M), while the bio-enhanced repair group and the ACL reconstruction group were hypervascular at both time points (I, K, L, & N).

Fig. 4

The mean total lesion areas for the four experimental groups (ACLT = ACL transection, ACLR = ACL reconstruction, BE-ACLR = bio-enhanced ACL reconstruction and BE-Repair = bio-enhanced ACL repair) at 6 and 12 months for the surgical and the ACL intact knee. The mean data are plotted with the 95% confidence intervals. Means that are significantly different after Holm adjustment are highlighted with *(p_adj<.05) or **(p_adj<.01). It should be noted that it was not appropriate to normalize the findings to the contralateral knee as there were significant differences in the contralateral knee between treatment groups both at 6 and 12 months (B).

Fig. 5

The distal femur cartilage 1-year after A) an untreated ACL rupture, B) after conventional ACL reconstruction, C) after bio-enhanced ACL repair, and D) after bio-enhanced ACL reconstruction. Note the damage to the medial femoral condyle in the untreated, ACL reconstructed knees, and bio-enhanced ACL reconstructed knees (black arrows), and the lack of damage in the medial femoral condyle in the bio-enhanced ACL repair and bio-enhanced ACL reconstructed knees (white arrow).